The field of the invention is spa controllers and the invention relates more particularly to the control of heaters for spas. Most electrically heated spas are equipped with an electric heating element that is nominally rated at 6 kw, at 240 volts. This same heater is rated at 1.5 kw at 120 volts. A typical spa installation operating at 240 volts requires a 50 amp service to provide enough current to operate the heater and the water and air pumps in the spa. The following table summarizes the current consumption in a typical spa with a heater, a dual speed water pump and an air blower:
Innovations in the spa industry have made it necessary to add a second and even a third water pump. Such additions require more current and, in order to stay within the limitations of the available current, it has become necessary for the spa heater to be turned off when the pumps are operating. With the heater turned off, the spa cools down and a user must turn off one or more pumps in order for the spa to reheat again.
In order to stay within the available current limitations, because of the limitations of the driving relays, some spas may be equipped with heaters that have lower wattage ratings. 4 kw and even 3 kw heaters are not uncommon in the spa industry. For larger or commercial institutions, an 11 kw heater is often used. This heater requires at least a 50 amp supply service just for operating the heater alone.
Modern spas typically utilize electronic controls. One such control system is shown in U.S. Pat. No. 5,361,215. Such systems, however, typically turn off the single spa heater when there is insufficient supply service. Alternatively, low kilowatt rated heaters are used which slow the initial heating of the spa.
It is an object of the present invention to provide a spa heating system which permits faster initial heating of the spa, as well as faster heat recovery under use, especially in colder weather.
It is another object of the present invention to provide a spa control system which permits heating while the spa is being used without the need for higher available current with its concomitant requirement for larger supply wire size and increase of power service to the residence.
The present invention is for a process for electrically heating a spa having electrically operated devices connected thereto, such as one or more water and/or air pumps, lights, and at least two heaters in an environment in which there is sufficient current available to operate all spa devices simultaneously. The process includes the steps of providing a control system with data as to which devices are connected to the spa and how much current each device requires, as well as the amount of current available to the spa. Next, the amount of current being used by devices other than the two heaters is calculated and subtracted from the available current to provide the value of residual current. If the spa water is in need of heating, a determination is made as to whether there is enough current available to operate one heater or both heaters, and the control system activates one or both heaters, based upon the results of this calculation.